Structures in superconducting YBa2Cu3O7−δ thin films investigated by magneto-optic technique

Using a reflection magneto-optic technique we have investigated natural inhomogeneities and artificial structures in YBCO thin films exposed to an external magnetic field. The artificial structures were mechanically scratched by scanning a diamond tip with different loading over the film surface. Alternatively planar structures with reduced oxygen content could be patterned by heating the YBCO film with a focused laser beam in nitrogen atmosphere. Depending on the laser annealing parameters different screening properties concerning the applied magnetic field could be achieved.As a magneto-optically active layer we used EuS films evaporated on glass as well as bismuth- and gallium-doped lutetium-iron-garnet films grown onto (111) oriented gadolinium-gal lium-gar net substrates by liquid phase epitaxy. In contrast to measurements with EuS films that show only weak faraday rotation for temperatures higher than 20 K the magneto-optic studies have been expanded to about 60 K by using the garnet films.     

Reduction of the temperature dependence of the nonreciprocal effect of magneto-optic channel waveguides

The nonreciprocal effect is the difference Deltabeta = beta(forward)-beta(backward) between forward and backward-propagation constants of optical modes. This effect is analyzed for the fundamental TM00 mode of channel waveguides in epitaxially grown magnetic garnet films. To increase |Deltabeta|, double layers with opposite signs of Faraday rotation are used to prepare the waveguides. It is shown that the temperature dependence of Deltabeta can be reduced considerably if the layer with positive Faraday rotation, which is at room temperature close to the Curie point, is replaced by a paramagnetic layer with negligible Faraday rotation. Concurrently, however, |Deltabeta| is decreased by approximately 35% at 295 K.     

Ein Beitrag zur quantitativen Analyse kleiner Schmierfettmengen mit papierchromatographischen Methoden

A Contribution on the Quantitative Analysis of Small Amounts of Lubricating Grease by Paper-Chromatographic Methods A method for paper-chromatographic determination of the ratio of soap: oil in lubricating greases is described; it operates with 10–50 mg samples and errors are of the order of ±1 wt.%. For selected lubricating greases, the alteration of soap: oil-ratio after mechanical-dynamic stress in ”?Kugelfischer”?-grease testing machine according to G. Spengler is investigated.     

Air plasma treatment of aluminium trihydrate filled poly(methyl methacrylate)

Air plasma treatments of aluminium trihydrate filled poly(methyl methacrylate) polymer (PMMA) composites were carried out in a dielectric barrier discharge. X-ray photoelectron spectroscopy (XPS) and attenuated total reflection – infrared spectroscopy have been employed to analyse the changes in chemical composition. Confocal laser-scanning microscopy and atomic force microscopy yielded the impact on surface structure and morphology. Surface free energy (SFE) measurements and adhesive bond strength tests were used to correlate the results to possible applications like gluing and lacquering. The plasma treatments resulted mainly in an etching of the matrix polymer and a minor chemical modification. An apparent contradiction of XPS, ATR and SFE results was attributed to a re-polymerization and re-deposition of the etched PMMA material as debris back onto the surface. This effect, which is seldom taken into account, annihilated the positive impact of the plasma treatment due to the debris acting as rated break point.     

Improved design of magnetooptic rib waveguides for opticalisolators

Garnet films of the following compositions (Lu,Bi)₃(Fe,Ga,Al)₅O₁₂ and (Tm,Bi)₃(Fe,Ga)₅O₁₂ are grown by liquid-phase epitaxy on [111]-oriented substrates of gadolinium gallium garnet. Double layers with opposite signs of Faraday rotation and single layers are prepared. Optical monomode rib waveguides are realized using such films. The nonreciprocal phase shift of the fundamental TM-mode is studied both theoretically and experimentally at a wavelength of 1.3 μm. The maximum nonreciprocal effect of double layer films is about 1.7 times larger than that of similar single layer waveguides. Agreement between experiments and calculations is excellent